Charged particle beam device and image processing method in charged particle beam device

ABSTRACT

There is provided a charged particle beam device which includes a charged particle beam source, a charged particle beam optical system that irradiates a sample with a charged particle beam from the charged particle beam source, a detector that detects a secondary signal generated from the sample by irradiation with the charged particle beam, and an image processing unit that executes integration processing of image data obtained from the secondary signal and outputting an integrated image, and in which the image processing unit executes a normalization integration computation of outputting an integrated image in which a luminance value of the integrated image is always “1” in an integration process.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/776,404 filed on May 15, 2018, which claims the benefit of priorityunder 35 U.S.C. § 119 of International Application No.PCT/JP2015/083488, filed on Nov. 27, 2015, the entire contents of whichare hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a charged particle beam device and animage processing method in the charged particle beam device.

BACKGROUND ART

A microscope or the like using a charged particle beam scans a samplewith the charged particle beam which the sample is irradiated in twodimensions of the horizontal direction and the vertical direction anddetects a secondary signal generated from an irradiation region. Themicroscope amplifies and integrates the detected signal by an electriccircuit and correlates the detected signal with scanning coordinates ofthe charged particle beam, thereby generating a two-dimensional image.

Here, regarding a device that performs image formation, an image formingmethod for improving a signal-to-noise ratio (S/N ratio) by integratinga plurality of pieces of two-dimensional image data is known. In PTL 1,PTL 2, PTL 3, PTL 4, and PTL 5, in order to suppress the influence ofnoise as described above, a technique in which the same imaging regionis scanned a plurality of times and adds and averages signals obtainedby the scanning is described. By performing adding and averaging, itbecomes possible to suppress irregularly occurring noise to some extent.

In PTL 1, a method of controlling a gain of a multiplier for integrationcomputation as an input pixel luminance value largely fluctuates due tothe influence of noise is described. In PTL 2, a method in which aplurality of frame memories necessary for frame integration are mounted,a frame image before two frames is also set as a target of integrationcomputation, and a multiplication rate thereof is switched is described.In PTL 3, a frame integration method in which an averaging arithmeticexpression of frame integration computation multiplied by an exponentand divided by the exponent is used as an arithmetic expression isdescribed. In PTL 4, a method of appropriately adjusting signalintensity of an image to be integrated is described. In PTL 5, a methodof detecting positional deviation and variably setting a frameintegration number with respect to the degree of positional deviation isdescribed.

CITATION LIST Patent Literature

PTL 1: JP-A-2010-182573

PTL 2: JP-A-2000-182556

PTL 3: JP-A-2008-186727

PTL 4: JP-A-9-330679

PTL 5: JP-A-2012-049049

PTL 6: JP-A-7-130319

SUMMARY OF INVENTION Technical Problem

In the conventional frame integration method, a frame-integrated imageis generated by dividing an input image by a frame integration numberwhich is set in advance and addition is made thereto by the integrationnumber. Accordingly, the conventional frame-integrated image isinitially in a dark state in an integration process and then graduallybecomes a bright state and thus, the user cannot confirm the image inthe integration process.

Accordingly, the present invention provides a technique for displaying aframe-integrated image with no sense of discomfort (no dark display) inthe integration process.

Solution to Problem

For example, in order to solve the problem described above, aconfiguration described in the claims is adopted. Although the presentapplication includes plurality of means for solving the problemdescribed above, as an example thereof, there is provided a chargedparticle beam device which includes a charged particle beam source, acharged particle beam optical system that irradiates a sample with acharged particle beam from the charged particle beam source, a detectorthat detects a secondary signal generated from the sample by irradiationwith the charged particle beam, and an image processing unit thatexecutes integration processing of image data obtained from thesecondary signal and outputting an integrated image, and in which theimage processing unit executes a normalization integration computationof outputting an integrated image in which a luminance value of theintegrated image is always “1” in integration process.

Also, according to another example, there is provided a charged particlebeam device which includes a charged particle beam source, a chargedparticle beam optical system for irradiating each of a plurality ofdivided regions in a sample with a charged particle beam from thecharged particle beam source, a detector for detecting a secondarysignal generated from each of the plurality of divided regions byirradiation with the charged particle beam, an image processing unit forexecuting integration processing of image data obtained from thesecondary signal and outputting an integrated image, and a display unitfor displaying the integrated image for each of the plurality of dividedregions, and in which the image processing unit determines the end ofthe integration processing according to image quality of the integratedimage for each of the plurality of divided regions.

According to still another example, there is provided an imageprocessing method in a charged particle beam device, which includes astep of irradiating a sample with a charged particle beam from thecharged particle beam source, by a charged particle beam optical system,a step of detecting a secondary signal generated from the sample byirradiation with the charged particle beam, by a detector, a step ofexecuting integration processing of image data obtained from thesecondary signal and outputting an integrated image, by an imageprocessing unit, and in which the outputting step includes executingnormalization integration computation of outputting an integrated imagein which a luminance value of the integrated image is always “1” inintegration process.

Advantageous Effects of Invention

According to the present invention, it is possible to display aframe-integrated image with no sense of discomfort (no dark display) inthe integration process. Further features relating to the presentinvention will become apparent from description of the presentspecification and accompanying drawings. Also, the problems,configurations, and effects other than those described above will beclarified by description of the following embodiments.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a configuration of a charged particlebeam device relating to conventional frame-integrated image acquisition.

FIG. 2 is an internal configuration diagram of a conventional imageprocessing unit.

FIG. 3 is a diagram for explaining conventional frame integrationcomputation.

FIG. 4 is a flowchart for explaining a conventional frame-integratedimage acquisition procedure.

FIG. 5 is a GUI when a conventional frame-integrated image is acquired.

FIG. 6 is a diagram illustrating a configuration of a charged particlebeam device relating to frame-integrated image acquisition of thepresent invention.

FIG. 7 is an internal configuration diagram of an image processing unitof the present invention.

FIG. 8 is a diagram for explaining frame integration computation of thepresent invention.

FIG. 9 is a flowchart for explaining a frame-integrated imageacquisition processing flow of the present invention.

FIG. 10 is a GUI when a frame-integrated image of the present inventionis acquired.

FIG. 11 is a diagram illustrating a display example of theframe-integrated image.

FIG. 12 is a flowchart for explaining an operation procedure offrame-integrated image acquisition of the present invention.

FIG. 13 is a GUI for selecting an image evaluation method of the presentinvention.

FIG. 14 is a diagram for explaining an image evaluation index (SNR).

FIG. 15 is a diagram for explaining the image evaluation index (SNR).

FIG. 16 is a diagram for explaining the image evaluation index (SNR).

FIG. 17 is a diagram for explaining another image evaluation index(degree of SN improvement).

FIG. 18 is a diagram for explaining the image evaluation index (degreeof SN improvement).

FIG. 19 is a diagram for explaining the image evaluation index (degreeof SN improvement).

FIG. 20 is a diagram for explaining the image evaluation index (degreeof SN improvement).

FIG. 21 is a diagram for explaining another image evaluation index(CNR).

FIG. 22 is a diagram for explaining the image evaluation index (CNR).

FIG. 23 is an internal configuration diagram of an image evaluation unitof the present invention.

FIG. 24 is a diagram for explaining a comparison between integratedimage display in an integration process of the prior art and that of thepresent invention.

FIG. 25 is a flowchart for explaining a processing flow of extremely lowmagnification image acquisition in which a conventional frame-integratedimage acquisition function is implemented.

FIG. 26 is a diagram for explaining an outline of scanning of extremelylow magnification image acquisition in which the conventionalframe-integrated image acquisition function is implemented.

FIG. 27 is a GUI when the conventional extremely low magnification imageis acquired.

FIG. 28 is a flowchart for explaining an operation procedure of theconventional extremely low magnification image acquisition.

FIG. 29 is a flowchart illustrating a processing flow of extremely lowmagnification image acquisition in which frame-integrated imageacquisition function of the present invention is implemented.

FIG. 30 is a diagram for explaining an outline of scanning of extremelylow magnification image acquisition in which the frame-integrated imageacquisition function of the present invention is implemented.

FIG. 31 is the GUI when the extremely low magnification image of thepresent invention is acquired.

FIG. 32 is a flowchart for explaining an operation procedure ofextremely low magnification image acquisition of the present invention.

FIG. 33 is a flowchart for explaining a processing flow of extremely lowmagnification image acquisition (integrated image parallel-acquisitiontype) in which the frame-integrated image acquisition function of thepresent invention is implemented.

FIG. 34 is a diagram for explaining an outline of scanning of extremelylow magnification image acquisition (integrated imageparallel-acquisition type) of the present invention.

FIG. 35 is a diagram for explaining the outline of scanning of extremelylow magnification image acquisition (integrated imageparallel-acquisition type) of the present invention.

FIG. 36 is a diagram for explaining the outline of scanning of extremelylow magnification image acquisition (integrated imageparallel-acquisition type) of the present invention.

FIG. 37 is a diagram for explaining the outline of scanning of extremelylow magnification image acquisition (integrated imageparallel-acquisition type) of the present invention.

FIG. 38 is a diagram for explaining the outline of scanning of extremelylow magnification image acquisition (integrated imageparallel-acquisition type) of the present invention.

FIG. 39 is a diagram for explaining the outline of scanning of extremelylow magnification image acquisition (integrated imageparallel-acquisition type) of the present invention.

FIG. 40 is a GUI when the extremely low magnification image (integratedimage parallel-acquisition type) of the present invention is acquired.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to the accompanying drawings. The accompanying drawingsillustrate specific examples according to the principle of the presentinvention, but these are for understanding of the present invention andare not used to limitedly interpret the present invention in any way.

The embodiments described below relate to an image forming apparatus forforming an image by integrating image data obtained by a chargedparticle beam device for scanning a charged particle beam at a highspeed, and more particularly to a function of forming an image byintegrating image data in units of frames.

Comparative Example

FIG. 1 is a diagram for explaining an outline of a scanning electronmicroscope, which is an example of a snorkel lens type scanning electronmicroscope (SEM).

The scanning electron microscope includes an electron optical systemconstituted with optical elements such as an electron gun 102, afocusing lens 104, a deflection coil 105, and an objective lens 106.

A sample 107 is disposed on a sample stage 108 in a vacuum column 101. Apredetermined position of the sample 107 is irradiated with an electronbeam 103 generated by the electron gun 102. The electron beam 103 isfocused by the focusing lens 104 and further narrowed by the objectivelens 106. The electron beam 103 is controlled to be deflected by thedeflection coil 105. Secondary electrons, reflected electrons, and othersecondary signals are generated from a surface of the sample 107irradiated with the electron beam 103. These secondary signals aredetected by a detector 110.

An information processing unit 117 is a control unit thatcomprehensively controls the scanning electron microscope. Theinformation processing unit 117 controls a lens control unit (notillustrated), a stage control unit 118, a deflection control unit 119,and an image processing unit 113 by a control signal 123.

For example, the information processing unit 117 includes a processor(also, referred to as a computation unit) and a storing unit (forexample, a memory or the like). The information processing unit 117 maybe realized by executing a program of desired computation processing bya processor.

The information processing unit 117 is connected to an information inputdevice 120. That is, the information processing unit 117 has aninterface with an external device. The information input device 120 is,for example, a keyboard, a mouse, or the like. The informationprocessing unit 117 is connected to an information transmissionapparatus 121. The information processing unit 117 displays a state ofeach portion which is a management target and the detected image on adisplay device (for example, a monitor or the like) of the informationtransmission apparatus 121.

The sample stage 108 is controlled by a stage control unit 118.Deflection of the electron beam 103 is controlled by a deflectioncontrol unit 119. The deflection control unit 119 controls a deflectioncurrent to be supplied to the deflection coil 105 to change magneticfield strength and causes the electron beam 103 to scan in thehorizontal direction and the vertical direction. The deflection controlunit 119 also supplies a signal (deflection signal 122) for controllingthe degree of deflection to an image processing unit 113. Lensintensities of the focusing lens 104 and the objective lens 106 areadjusted by a lens control unit (not illustrated). The image processingunit 113 detects the secondary signal generated in synchronization withscanning by the deflection signal through the detector 110.

The signal detected by the detector 110 is amplified by an amplifier 111and converted into a digital signal by an analog-to-digital converter(ADC) 112. Image data converted to digital is input to a multiplier 115in the image processing unit 113. The multiplier 115 multiplies imagedata converted to digital described above by a coefficient K1. Thecoefficient K1 is set by the image processing unit 113. The multipliedimage data is input to an adder 116. The adder 116 adds the input imagedata and image data read from a frame memory 114, and outputs the addedimage data 124 to the frame memory 114 and the information processingunit 117.

The image processing unit 113 stores the image data 124 in the framememory 114. In this case, the image processing unit 113 receives thedeflection signal from the deflection control unit 119 as describedabove, and generates an address (pixel unit) of the two-dimensionalcoordinate for storing image data in the frame memory based on thedeflection signal. According to this address, the image processing unit113 stores the image data 124 output from the adder 116 in the framememory 114. Similarly, the image processing unit 113 reads image datastored in the frame memory 114 according to the address of thetwo-dimensional coordinate and inputs the image data to the adder 116.The information processing unit 117 outputs the image data 124 to thedisplay unit of the information transmission apparatus 121.

Next, a conventional integration processing will be described based onthe configuration described above. Since the multiplier 115, the adder116, and the frame memory 114 are configured as described above, theimage data detected by the detector 110 according to deflection controland image data one scan before (one frame before) stored in the framememory 114 are input to the adder 116. The image data detected by thedetector 110 is multiplied by the coefficient K1 by the multiplier 115.Here, the coefficient K1 is a reciprocal of an integration number N.

FIG. 2 is an internal configuration diagram of the image processing unit113 and FIG. 3 is an expression expressing integration process.I_(i)(x,y) represents pixel data corresponding to x, y coordinates.I_(i)(x,y) is input to a multiplier 201. The multiplier 201 multipliesI_(i)(x,y) by the coefficient K1 (1/N), and outputs multiplied data toan adder 202. S_(i)(x,y) represents pixel data corresponding to the x, ycoordinates of the i-th frame input to a frame memory 203. S_(i-1)(x,y)represents pixel data corresponding to the x, y coordinates of the(i−1)-th frame output from the frame memory 203. A calculationexpression of S_(i)(x,y) is as expressed in Expression (1-a) of FIG. 3.The adder 202 executes integration processing of the multiplied data(I_(i)(x,y)/N) and the pixel data S_(i-1) (x, y) one frame before, andthe pixel of the i-th frame and outputs data S_(i)(x,y).

The calculation expression of the integrated pixel data S_(N)(x,y) is asexpressed in Expression (1-b) of FIG. 3. S_(N)(x,y) means that pixeldata corresponding to the x, y coordinates of an input frame is addedfrom a first frame to an integration number N-th frame and is divided bythe integration number N. The image processing unit 113 multiplies inputpixel data by a reciprocal of the integration number N and adds themultiplied pixel data by the number of integration N times, therebyaveraging processing of the pixel data.

Due to the computation processing described above, a luminance value ofaveraged pixel data becomes a luminance value “1” to be obtainedoriginally when addition of an N-th integration is completed. In thepresent specification, the luminance value “1” defines a luminance valueof a pixel obtained when the luminance value of the input pixel is addedN times and is divided by N as “1”.

As is generally known, detection signals such as reflected electrons andsecondary electrons are invariable in time and thus, correlation betweenframes is extremely large. In contrast, noise generated in a process ofsignal detection often contributes randomly and there is almost nocorrelation between frames. Accordingly, it is possible to reduce noisecomponents and improve the S/N ratio of the image can be improved by anaveraging processing (frame integration processing) between frames.

FIG. 4 illustrates an operation flow for obtaining a frame-integratedimage using a frame integration circuit having the configurationdescribed above after an observation region for which a frame-integratedimage is intended to be acquired is determined by searching a viewingfield. FIG. 5 illustrates a graphical user interface (GUI) for acquiringframe-integrated images.

A screen 401 is displayed on the display device of the informationtransmission apparatus 121. The user starts acquiring theframe-integrated image (STEP 301). Next, the user inputs a frameintegration number for the observation region to a setting unit 402, andpresses a setting button 403 (STEP 302). In this case, when theintegration number is small, an image with poor S/N ratio may beobtained. When the integration number is large, by excessive electronbeam irradiation, sample destruction can be caused, contamination can begenerated, a sample can be charged up, or an image on which theinfluence of luminance value saturation and drift is superimposed can beobtained. The user needs to set an optimal integration number forobtaining an image having image quality expected by the user, but it isdifficult to ascertain the optimal integration number in advance.

After setting the integration number, the user presses aframe-integrated image acquisition button 405 to execute integratedimage acquisition (STEP 303). The scanning electron microscope executesa frame integration scan and an integration computation process. Theframe-integrated image is displayed on an image display window 404 (STEP304). The user confirms whether the image displayed on the image displaywindow 404 is the image having image quality expected by the user (STEP305). When it is an image having the image quality expected by the user,the frame-integrated image acquisition is ended (STEP 306). However,when it is not the image having the image quality expected by the user,it is necessary to reset the integration number again, execute screenacquisition, and confirm an acquired image (STEP 302 to STEP 305). Theuser needs to repeat operations of STEP 302 to STEP 305 until the imagehaving the image quality expected by the user can be acquired.

The frame integration number to be set is greatly influenced bycomposition elements and structures of the sample and observationconditions (accelerating voltage, irradiation yield, degree of vacuum,working distance (WD), and the like). For that reason, it is difficultto ascertain the optimum integration number considering the structure ofthe sample and observation conditions when the frame-integrated image isacquired. Accordingly, conventionally, cases where the operations ofSTEP 302 to STEP 305 are repeated to obtain the optimum integrationnumber to acquire the frame-integrated image often occur.

As a result, conventionally, there were the following problems.

(a) It takes time and effort to perform repetitive image acquisition.

(b) Since image acquisition is repeatedly performed, the imageacquisition time increases.

(c) The electron beam irradiation time for the sample is increased(electron beam irradiation amount increases) by the b. There is a highpossibility of causing secondary problems such as an increase in theamount of electron beams with which the sample is to be irradiated,causing sample destruction, causing occurrence of contamination, andcharging the sample.

In the method described above, for the frame-integrated image, the inputpixel data is divided by a frame integration number N which is set inadvance and integration processing with pixel data one frame past isexecuted. This integration processing is repeated until the N-th frame.Here, when it is assumed that definition of the luminance value “1” isas described above, the luminance value of the frame-integrated image ofa first frame becomes 1/N and a frame-integrated image up to a secondframe is 2/N. Accordingly, the luminance value of the conventionalframe-integrated image becomes the “number of input images/integrationnumber N” in the integration process. Therefore, in order for theluminance value to be “1”, it is necessary to wait for integrationprocessing up to the N-th frame. As such, since the conventionalframe-integrated image is initially in a dark state in the integrationprocess and thereafter gradually becomes a bright state, the user cannotconfirm the image in the integration process.

First Embodiment

In the following, embodiments for solving the above problem will bedescribed. FIG. 6 illustrates an example of a charged particle beamdevice according to a first embodiment, which is an example of a snorkellens type scanning electron microscope (SEM).

In the following description, a scanning electron microscope, which isan example of a charged particle beam device, will be described as anexample, but is not limited thereto. The present invention can also beapplied to other charged particle beam devices such as an ion beamapparatus for synthesizing secondary signals such as images to form acombined signal.

Means for realizing an image processing part in the following embodimentmay be subjected to function realization by software or by hardware. Inthe following example, function realization by hardware will bedescribed.

The scanning electron microscope includes an electron optical system(charged particle beam optical system) constituted with optical elementssuch as an electron gun (charged particle beam source) 502, a focusinglens 504, a deflection coil 505, and an objective lens 506. The electronbeam optical system may include other constituent elements (lens,electrode, and the like) other than the components described above, andis not limited to the configuration described above.

A sample 507 is disposed on a sample stage 508 in a vacuum column 501. Apredetermined position of the sample 507 is irradiated with an electronbeam 503 generated by the electron gun 502. The electron beam 503 isfocused by the focusing lens 504 and further narrowed by the objectivelens 506. The electron beam 503 is controlled to be deflected by thedeflection coil 505. Secondary electrons, reflected electrons, and othersecondary signals are generated from a surface of the sample 507irradiated with the electron beam 503. These secondary signals aredetected by a detector 510.

An information processing unit 517 is a control unit thatcomprehensively controls the scanning electron microscope. Theinformation processing unit 517 controls a lens control unit (notillustrated), a stage control unit 518, a deflection control unit 519,an image processing unit 513, and an image evaluation unit 522 by acontrol signal 523.

For example, the information processing unit 517 includes a processor(also, referred to as a computation unit) and a storing unit (forexample, a memory or the like). The information processing unit 517 maybe realized by executing a program of desired computation processing bya processor.

The information processing unit 517 is connected to an information inputdevice 520. That is, the information processing unit 517 has aninterface with an external device. The information input device 520 is,for example, a keyboard, a mouse, or the like. The informationprocessing unit 517 is connected to an information transmissionapparatus 521. The information processing unit 517 displays a state ofeach portion which is a management target and the detected image on adisplay device (for example, a monitor or the like) of the informationtransmission apparatus 521.

The image processing unit 513 executes integration processing of theimage data obtained from the secondary signal and outputs an integratedimage. The image processing unit 513 includes a frame memory 514, amultiplier 515, a multiplier 525, and an adder 516.

The sample stage (stage) 508 is controlled by a stage control unit 518.Deflection of the electron beam 503 is controlled by a deflectioncontrol unit 519. The deflection control unit 519 controls a deflectioncurrent to be supplied to the deflection coil 505 to change magneticfield strength and causes the electron beam 503 to scan in thehorizontal direction and the vertical direction. The deflection controlunit 519 also supplies a signal (deflection signal 524) for controllingthe degree of deflection to an image processing unit 513. Lensintensities of the focusing lens 504 and the objective lens 506 areadjusted by a lens control unit (not illustrated). The image processingunit 513 detects the secondary signal generated in synchronization withscanning by the deflection signal through the detector 510.

The signal detected by the detector 510 is amplified by an amplifier 511and converted into a digital signal by an ADC 512. Image data convertedto digital is input to a multiplier 515 in the image processing unit513. The multiplier 515 multiplies image data converted to digitaldescribed above by a first coefficient K₂ and outputs first image data(K₂×image data). The first coefficient K₂ is set by the image processingunit 513. The first image data (K₂×image data) is input to the adder516. The image data 527 one frame past is input from a frame memory 514to a multiplier 525. The multiplier 525 multiplies image data 527 onescan before (one frame before) by a second coefficient K₃ and outputssecond image data (K₃×image data). The second coefficient K₃ is set bythe image processing unit 513. The second image data (K₃×image data) isinput to the adder 516. The adder 516 adds the first image data(K₂×image data) from the multiplier 515 and the second image data(K₃×image data) from the multiplier 525, and adds added image data 528to the frame memory 514, the information processing unit 517, and theimage evaluation unit 522.

The image processing unit 513 stores the image data 528 in the framememory 514. In this case, the image processing unit 513 receives thedeflection signal from the deflection control unit 519 as describedabove, and generates an address (pixel unit) of the two-dimensionalcoordinate for storing image data in the frame memory 514 based on thedeflection signal. According to this address, the image processing unit513 stores the image data 528 output from the adder 516 in the framememory 514. The information processing unit 517 outputs the image data528 to a display unit of the information transmission apparatus 521. Theimage evaluation unit 522 evaluates the image data 528 and outputs anevaluated result 526 to the information processing unit 517. Theinformation processing unit 517 controls an integration scan andintegration processing of the image processing unit 513 based on theevaluated result 526.

Next, integration processing of the present embodiment will be describedbased on the configuration described above. FIG. 7 is an internalconfiguration diagram of the image processing unit 513 and FIG. 8 is anexpression representing integration processing. The image processingunit 513 includes an integration counter 601, a first coefficientcalculation unit 602, a second coefficient calculation unit 603, amultiplier 604, a multiplier 605, an adder 606, and a frame memory 607.

I_(i)(x,y) represents pixel data corresponding to the x, y coordinatesof an i-th frame input from the detector 510 via the amplifier 511 andthe ADC 512. I_(i)(x,y) is input to the multiplier 604. The integrationcounter 601 counts and identifies what frame number of image data thatis currently detected and inputted based on the deflection signal inputfrom the deflection control unit 519. The integration counter 601outputs a frame count value i to the first coefficient calculation unit602. The first coefficient calculation unit 602 outputs the reciprocalof the input frame count value i as a first coefficient K₂ (Expression(6-d) in FIG. 8). The first coefficient calculation unit 602 outputs thefirst coefficient K₂ to the multiplier 604 and the second coefficientcalculation unit 603. The second coefficient calculation unit 603calculates a second coefficient K₃ based on the value of the firstcoefficient K₂. The second coefficient K₃ is calculated as in Equation(6-e) in FIG. 8. Accordingly, the sum of the first coefficient K₂ andthe second coefficient K₃ is 1 (K₂+K₃=1) (Expression (6-c) in FIG. 8).

The multiplier 604 multiplies I_(i)(x,y) by the first coefficient K₂ andoutputs multiplied data to the adder 606. S_(i)(x,y) represents pixeldata corresponding to the x, y coordinates of the i-th frame input tothe frame memory 607. Also, S_(i-1)(x,y) represents pixel datacorresponding to the x, y coordinates of the (i−1)-th frame from theframe memory 607. The multiplier 605 multiplies (x,y) by the secondcoefficient K3 and outputs multiplied data to the adder 606. Thecalculation expression of S_(i)(x,y) is as illustrated in Equation (6-b)in FIG. 8. The adder 606 executes integration processing of themultiplied data (K₂×I_(i)(x,y)) and the multiplied data (K₃×S_(i-1)(x,y)) and outputs i-th frame pixel data S_(i)(x,y).

From the matters as described above, the first coefficient K₂ and thesecond coefficient K₃ vary according to the input frame count value i ofthe integration counter 601. The sum of the first coefficient K₂ and thesecond coefficient K₃ is always “1”. This means that the luminance valueof the integrated image is always “1” in the integration process. Thatis, in the present embodiment, a normalization process (hereinafter,referred to as a normalization integration computation) is realized insuch a way that the luminance value of the integrated image is always“1” in the integration process. From the matters as described above,matters in which the integration computation result is represented inthe case where the integration number is N is expressed in Equation(6-f) in FIG. 8 based on the normalization integration computation. Thiscomputation result is exactly the same integration result as theconventional frame integration computation result illustrated inEquation (1-b) in FIG. 3, and averaging processing of pixel data similarto the conventional frame integration computation is realized.

From the matters as described above, the frame normalization integrationcomputation of the present embodiment is a method that can always outputthe integrated image being integrated with its luminance value which isin a state of being “1”, in addition to averaging processing of imageluminance values which the conventional frame integration computation isrealizing.

Next, while illustrating an internal processing flow and an operationflow of the user, the means for realizing the image acquisition by theframe normalization integration computation of the present embodimentand the effect thereof will be described in detail. FIG. 9 illustrates aprocessing flow for obtaining a frame-integrated image using a frameintegration circuit having the configuration described above. FIG. 10illustrates a GUI for acquiring the frame-integrated image. FIG. 12illustrates the operation flow of the user.

A screen 801 is displayed on a display device of the informationtransmission apparatus 521. When an observation region for which aframe-integrated image is intended to be acquired is determined, theuser executes image acquisition (STEP 701). An execution instruction isinput from the information input device 520 to the informationprocessing unit 517, and the integration scan by one frame is executed(STEP 702).

Detected image data is input to the image processing unit 513, and thenormalization integration computation described above is appliedthereto. In this case, a count value of the integration counter 601becomes “1”, and it is recognized as an integrated image of the firstframe. A value corresponding to the first frame is set for the firstcoefficient K₂ and the second coefficient K₃, and the integrationcomputation is performed. After the normalization integrationcomputation, the image processing unit 513 outputs frame-integratedimage data to the frame memory 514, the information processing unit 517,and the image evaluation unit 522. The frame-integrated image dataoutput to the frame memory 514 is stored in the frame memory 514 asintegrated image data of the first frame (integrated image data to whichone-time integration is applied). The integrated image data output tothe information processing unit 517 is transferred to the informationtransmission apparatus 521 and displayed as a frame-integrated image inan image display window 805.

The image evaluation unit 522 evaluates the input frame-integrated imagedata (STEP 703). The image evaluation unit 522 determines whether theframe-integrated image data obtained by the normalization integrationprocess satisfies a certain evaluation condition or not. When the imageis better than an image having image quality expected by the user (forexample, when the frame-integrated image data satisfies the evaluationcondition described later), the image evaluation unit 522 transmits ascan stop instruction to the information processing unit 517 (STEP 704).When the stop instruction is received, the information processing unit517 stops the integration scan and ends acquisition of theframe-integrated image (STEP 705).

On the other hand, in a case where the image is not better than an imageexpected by the user, the image evaluation unit 522 transmits aninstruction to continue the integration scan to the informationprocessing unit 517, and the information processing unit 517 executesthe integration scan for the next frame (Step 702). Image data of thesecond frame detected by the second the integration scan is input to theimage processing unit 513, and the normalization integration computationdescribed above is applied thereto. In this case, the count value of theintegration counter 601 becomes “2”, which is recognized as anintegrated image of the second frame. For the first coefficient K₂ andthe second coefficient K₃, values corresponding to the second frame areset and is subjected to integration computation. After the normalizationintegration computation, the image processing unit 513 outputsframe-integrated image data to the frame memory 514, the informationprocessing unit 517, and the image evaluation unit 522. The integratedimage data output to the frame memory 514 is stored in the frame memory514 as integrated image data of the second frame (integrated image datato which integration is applied twice). The integrated image output tothe information processing unit 517 is transferred to the informationtransmission apparatus 521 and displayed as a frame-integrated image inthe image display window 805.

The image evaluation unit 522 evaluates the input secondframe-integrated image (STEP 703). In a case where the integrated imageis better than an image having image quality expected by the user (forexample, in a case where the frame-integrated image data satisfies anevaluation condition to be described later), the process proceeds toSTEP 704, and in a case where the image is not good, the process returnsto STEP 702 again. The process of STEP 702 to STEP 703 is repeated untilthe frame-integrated image becomes better than the image having imagequality expected by the user. That is, the image processing unit 513repeatedly executes the normalization integration computation until theevaluation condition is satisfied. In this case, each time the processdescribed above is repeated, the count value of the integration counter601 of the normalization integration computation unit is incremented by1, and the frame integration number i is incremented.

From the matters as described above, in the present embodiment, imageevaluation is performed on the integrated image being integrated, andintegration processing (the integration scan and integrationcomputation) is ended at the time when an expected image is obtained.When automatic evaluation is performed, it is possible to realizeframe-integrated image acquisition without being conscious of the numberof integration (it is not necessary to set the integration number). Thisis because an image with the luminance value which is in a state ofbeing “1” can be output during integration by the normalizationintegration computation. The point of the present embodiment is that theintegrated image has the luminance value which is in a state of being“1” can be output during the integration and evaluation can be performedon the integrated image with its luminance value which is in a state ofbeing “1” during the integration.

Next, an operation flow of FIG. 12 will be described together with anoperation of the screen of FIG. 10. A screen 801 includes a frameintegration mode setting portion 802, a frame integration number displayportion 804, an image display window 805, an image acquisition executionbutton 806, an evaluation method setting button 808, and an integratedimage evaluation value display portion 809.

When an observation region for which a frame-integrated image isintended is determined, the user performs various settings on the screen801 and executes image acquisition (STEP 901). In the frame integrationmode setting portion 802, it is possible to select either an automaticmode or an integration number designation mode.

The automatic mode is a mode for performing automatic evaluation by theimage evaluation unit 522. The user sets an image evaluation method in acase of selecting the automatic mode. The user clicks the evaluationmethod setting button 808. FIG. 13 illustrates an evaluation methodsetting window 1001. When the evaluation method setting button 808 isclicked, the evaluation method setting window 1001 is displayed. Theevaluation method setting window 1001 includes an evaluation methodselection portion 1002 and an evaluation reference value setting portion1003. The user selects an evaluation method in the evaluation methodselection portion 1002. Details of various evaluation methods displayedhere will be described later. With this, it is possible to select anappropriate evaluation method depending on what image the user intendsto acquire in image acquisition (according to the definition of theimage having image quality expected by the user). Thereafter, the userinputs an evaluation reference value to the evaluation reference valuesetting portion 1003. The evaluation reference value input here is athreshold value for determining whether it is image quality expected bythe user. The user inputs the evaluation reference value to theevaluation reference value setting portion 1003, and then clicks thesetting button 1004. The user can also reset the evaluation referencevalue to a default value of an apparatus device by using the resetbutton 1005. In this case, a default evaluation reference value storedin the information processing unit 517 may be set again in the imageevaluation unit 522.

The integration number designation mode is a mode in which a frameintegration number is designated in advance. In the case of theintegration number designation mode, the user inputs the integrationnumber to the integration number setting portion 803. In this case,integration processing may be executed up to a set integration number,and the integrated image may be evaluated by the user himself/herself.

After the setting described above is ended, the user clicks the imageacquisition execution button 806 to obtain a frame-integrated image(STEP 902). In both the automatic mode and the integration numberdesignation mode, the frame-integrated image is displayed in the imagedisplay window 805 for one frame. The integration number of theframe-integrated images is displayed on the frame integration numberdisplay portion 804. In a case where the automatic mode is set, anevaluation value of the selected evaluation method is displayed on theintegrated image evaluation value display portion 809. With theconfiguration as described above, the user can confirm theframe-integrated image, the integration number, and the evaluation valuefor one frame.

As another example, at the time when integration processing is executedframe by frame and an integrated image displayed in the image displaywindow 805 becomes image quality expected by the user, a function ofstopping integration processing by the user's input may be provided.With this the user can stop integration processing (the integration scanand integration computation) while viewing the frame-integrated image inthe integration process.

As described above, in the case of the automatic mode, the user canacquire the frame-integrated image only by the operation of “imageacquisition execution” without being never conscious of the setting ofthe integration number. That is, it is not necessary to set the frameintegration number. In conventional frame integration processing, in acase where an image having image quality expected by the user cannot beobtained, the integration number has to be set again and a plurality ofimage acquisition have to be executed. In contrast, in frame integrationprocessing of the present embodiment, it is possible to acquire aframe-integrated image by one image acquisition operation. With this, itis possible to greatly improve time and effort for acquiring theframe-integrated image. It is possible to greatly reduce the timerequired for image acquisition.

The present embodiment has the following effects.

(a) In contrast to the conventional plural image acquisition operations,in the present embodiment, a frame-integrated image is obtained by oneimage acquisition operation.

(b) In the present embodiment, it is possible to perform the integrationscan with the minimum required number of integration by one imageacquisition operation.

(c) By both effects described above, it is possible to reduce theirradiation time of the electron beam with which the sample isirradiated as much as possible.

(d) By suppressing the amount of electron beam with which the sample isirradiated to be minimized, it is possible to obtain secondary effectsthat suppresses sample destruction, contamination generation, generationof luminance value saturation and drift due to the influence of chargingto be minimized.

Next, the definition of the “image having image quality expected by theuser” described above will be described. As an image having imagequality expected by the user, for example, an image having a good SNratio, an image in which the degree of SN improvement is saturated, animage without an influence of charge (an image without luminance valuesaturation due to charge, an image without drift due to charge), and thelike are included. In the present embodiment, the definition of the“image having image quality expected by the user” is switched accordingto what image the user intends to acquire in the image acquisition.

FIG. 11 illustrates another example of the image display window 805.Information other than the frame-integrated image may be displayed inthe image display window 805. For example, an image evaluation value(numerical value) 811 and an image evaluation graph 812 to be describedbelow may be displayed in the image display window 805.

Next, an image evaluation method will be described. An execution subjectof an evaluation process described below is the image evaluation unit522. As the image evaluation method, for example, an evaluation methodusing the SN ratio as an evaluation index, an evaluation method usingthe degree of SN improvement as an evaluation index, an evaluationmethod using a contrast-to-noise ratio (CNR) as an image noiseevaluation index, an evaluation method using a histogram as anevaluation index, and the like are included. Accordingly, the evaluationcondition of the integrated image is one of the condition using the SNratio as the evaluation index, the condition using the degree of SNimprovement as the evaluation index, the condition using thecontrast-to-noise ratio (CNR) as the image noise evaluation index, thecondition using the histogram as the evaluation index or a combinationthereof may be adopted.

FIG. 14 to FIG. 16 are diagrams for explaining the image evaluationindex (SNR). In the case where the SN ratio is used as an evaluationindex, an image without noise (or an image having little noise anddetermined as good by the user) is acquired in advance as a referenceimage 1101 (FIG. 14). A frame-integrated image 1102 to which thenormalization integration computation described above is applied isobtained (FIG. 15). The image evaluation unit 522 calculates the SNratio between the reference image 1101 and the frame-integrated image1102 (FIG. 16). When the calculated SN ratio reaches a value equal to orgreater than a SN ratio (evaluation reference value) by the user, theintegration scan and integration computation is ended.

FIGS. 17 to 20 are diagrams for explaining the image evaluation index(degree of SN improvement). The degree of SN improvement means thedegree of the difference in luminance value between the currentintegrated image and the integrated image one frame before. Thedifference value is used as an evaluation index. Matters that thedifference value becomes smaller is assumed that the SN ratio of eachintegrated image becomes better. That is, it is a method of indirectlydetermining the state of the SN ratio of each integrated image byrepresenting (quantifying) the degree of S/N ratio improvement betweenthe integrated images by the difference value of the luminance value ofthe integrated image and using this difference value as an evaluationindex (using the degree of SN ratio improvement as an evaluation index).

That is, the SN ratio is indirectly evaluated using the followingrelationship.

The SN ratio of each integrated image is improved.

The luminance value of each integrated image is focused on the signalcomponent (there is no noise component).

The luminance value difference between the integrated images becomeszero.

In FIG. 17, the reference numeral 1201 denotes the difference valueδ_(i) of the luminance value between frames in the process of performingthe integration processing using the integration number N. FIG. 18illustrates an expression of the difference value δ_(i)(x, y) of theluminance value. δ_(i)(x, y) represents the difference between S_(i)(x,y) and S_(i-1) (x, y) corresponding to the x and y coordinates.

FIG. 19 illustrates a graph 1202 illustrating the relationship of thedifference value of the luminance value with respect to the number oftimes of integration. As illustrated in the graph 1202, the imageevaluation unit 522 may determine whether the difference value of theluminance value is less than a predetermined threshold value δth. Theimage evaluation unit 522 may use an inclination of a curve as anevaluation index, and determine whether the inclination is less than apredetermined threshold value. In a case where the conditions describedabove are satisfied, the integration scan and the integrationcomputation are ended.

FIG. 20 illustrates an example 1203 in which a range is set for athreshold value. A range designation to some extent may be performedwith respect to a threshold value of the difference value of theluminance value and a threshold value of the inclination. Thecharacteristics of the relationship between the difference value of theluminance value and the number of times of integration varies dependingon an observation sample and an observation condition (opticalcondition). Accordingly, as illustrated in FIG. 20, the evaluationreference value may not be fixed and an evaluation condition having acertain range may be set.

FIGS. 21 to 22 are diagrams for explaining the image evaluation index(CNR: Contrast-to-noise ratio). This evaluation method is a method ofdetermining a noise amount of image using the CNR. Naturally, thedetected signal is represented as a luminance value in the image. Theamount of noise is evaluated by using a luminance value contrast of anoise-free signal component (grayscale difference in a luminance valuebetween a pixel having the largest signal amount and a pixel havingsmallest signal amount) and luminance value variation which is the noisecomponent. The image evaluation unit 522 may calculate the CNR in eachintegrated image and compare the CNR with the evaluation reference. Theimage evaluation unit 522 may determine that the integrated imageexpected by the user is acquired at the time when the CNR exceeds theevaluation reference value.

Next, a histogram evaluation method will be described. In a case where ahistogram of luminance values is used as an evaluation index, ahistogram representing a frequency distribution of luminance values ofpixels constituting a frame image is used. The image evaluation unit 522may evaluate at least one of the expected grayscale, the degree of noiseremoval, brightness, and contrast using statistical values such as anaverage value and standard deviation of the histogram. The imageevaluation unit 522 may determine that the integrated image that isequal to or greater than the image quality expected by the user isacquired if the statistical value exceeds a fixed evaluation referencevalue.

FIG. 23 illustrates an internal configuration of the image evaluationunit 522. The image evaluation unit 522 includes the functions describedin the example described above, that is, a histogram evaluation module1401, an SN ratio evaluation module 1402, an SN improvement degreeevaluation module 1403, and a CNR evaluation module 1404. Theinformation processing unit 517 transmits an evaluation method which isset by the evaluation method selection portion 1002 to the imageevaluation unit 552. The image evaluation unit 522 selects an evaluationmodule corresponding thereto and executes image evaluation of inputintegrated image data 1411. The image evaluation unit 522 returns anevaluation result 1412 to the information processing unit 517.

Although the evaluation reference value used by the image evaluationunit 522 at the time of image evaluation is prepared in the apparatus inadvance, the reference value may be changed by the user. With this, itis possible to acquire a frame-integrated image that is close to animage expected by the user.

In the automatic mode, in order to avoid that the evaluation value doesnot reach the evaluation reference value even if integration processingis repeated and the frame-integrated image cannot be acquired forever,an upper limit value of the integration number may be set in theinformation processing unit 517. In a case where the upper limit valueof the integration number reaches the upper limit value (in a case wherea count value of the integration counter 601 reaches the upper limitvalue), the information processing unit 517 may forcibly end acquisitionof the integrated image. For ease of use, it is also possible toconsider a case the user may want to acquire an integrated image with aslittle noise as possible by setting the integration number to large. Inthis case, the upper limit of the number of integration may be set tolarge.

In the present embodiment, a frame normalization integration functioncapable of computing (outputting) the luminance value of the integratedimage always in a state of “1” in the frame integration process and animage evaluation function capable of performing image evaluation of theintegrated image in the frame integration process, and it is possible toautomatically end the frame-integrated image acquisition process at thetime when the integrated image expected by the user is obtained.

In the present embodiment, the user can confirm information on therelationship between the frame-integrated image and the integrationnumber. This has the following advantages.

(a) It is possible to obtain reference information at the time ofacquiring an image using conventional frame-integrated image acquisition(integration number designation mode).

(b) It is possible to know the relationship between occurrence of sampledestruction, occurrence of contamination, luminance value saturation,and drift caused by charging and the integration number, as referenceinformation.

(c) It is possible to know the relationship between the integrationnumber and image evaluation information, and the relationship betweenthe integration number and the degree of improvement in the integrationprocess.

FIG. 24 is a diagram for explaining the effect of display in the frameintegration process of the present embodiment. In the framenormalization integration computation of the present embodiment, anintegrated image of luminance value 1 even during integration can beoutput. Conventionally, when acquisition of a frame-integrated imagehaving a large number of integration numbers is performed, in imagedisplay being integrated, as illustrated in the upper part of FIG. 24,dark display continues for a long time period of several tens of secondsfrom the start of integration, there was a problem of giving a sense ofdiscomfort to the user. In contrast, in the frame normalizationintegration computation of the present embodiment, since the integratedimage in the state can be instantaneously displayed from the first startof integration, as illustrated in the lower part of FIG. 24, imagedisplay without giving a sense of discomfort to the user is possible.

Conventionally, since the luminance value at the start of integration isnot “1” as described above, it was image display by which it wasdifficult to confirm the S/N improvement process by integrationcomputation. In contrast, in the present embodiment, the S/N improvementprocess can also be confirmed and usability is further improved.

Second Embodiment

In this embodiment, an example in which the frame-integrated imageacquisition function of the first embodiment is applied to an extremelylow magnification image creation function will be described.

In general, an electron microscope such as an SEM is effective forobservation at high magnification, but display with low magnification isnot good. The magnification of the electron microscope can be displayedat a maximum of several ten thousand times to several hundreds ofthousands times or several million times, whereas the lowestmagnification is on the order of several times to several tens of times.For example, the lowest magnification observable with the SEM isgenerally about 5 to 50 times. If the whole sample can be observed atlowest magnification, the viewing field search can be gradually shiftedto high magnification from the state in which the viewing field iswidened, that is, from the state in which it is displayed at lowmagnification, and gradually narrows the viewing field. However, if theentire sample cannot be observed even at the lowest magnification, it isnecessary to move the stage and perform the viewing field search, and awork to finally find a place intended to be observed on the samplebecomes difficult.

Accordingly, PTL 6 has been proposed as a solution method for theviewing field search in a condition that the entire region of the samplecannot be observed even at the lowest magnification. This is to dividethe sample into a plurality of regions, acquire respective observationimages, and join the observation images on a memory so as to create anextremely low magnification image of the entire sample, therebyovercoming the problem described above. Firstly, this overview will bedescribed.

Since an example of a configuration of the charged particle beamapparatus described here is the same as that in FIG. 1, the descriptionthereof will be omitted. Further, frame integration processing here isthe same as that described in FIGS. 2 and 3.

FIG. 25 illustrates a processing flow of creating a conventionalextremely low magnification image, and FIG. 26 illustrates an outline ofscanning of creating an extremely low magnification image. FIG. 27illustrates a GUI for acquiring an extremely low magnification image.

A screen 1801 is displayed on the display device of the informationtransmission apparatus 121. The user decides the observation region forwhich the frame-integrated image is intended to be acquired, performsvarious setting, and then executes low magnification image acquisition(STEP 1601). When an execution instruction is received, the informationprocessing unit 117 moves the sample stage (stage) 108 to the initialcoordinates via the stage control unit 118 based on coordinate data seton the screen 1801 (STEP 1602).

Next, the information processing unit 117 sets the coefficient K1 of themultiplier 115 based on the frame integration number set on the screen1801. The information processing unit 117 sets the scanning speed(integration number) and the number of scanning lines in the deflectioncontrol unit 119 (STEP 1603). Next, the information processing unit 117sets a recording range of the frame memory 114 (STEP 1604). Theinformation processing unit 117 sets a recording start point of theframe memory 114 in a region corresponding to the stage position (STEP1605).

Next, the image processing unit 113 executes conventional frameintegration processing (FIGS. 2 and 3) and stores the frame-integratedimage in the frame memory 114 (STEP 1606). FIG. 26 illustrates anexample in which the sample is divided into a plurality of regions. Inthis example, the sample is divided into 16 regions. An imageacquisition target region at this time is region 1 (1701). The imageprocessing unit 113 performs conventional frame integration processing(FIG. 2 and FIG. 3) for the region 1 (1701).

When the frame-integrated image acquisition is completed, theinformation processing unit 117 confirms whether the stage position isthe final region 16 (1703) or not (STEP 1607). In a case where it is thefinal region 16 (1703), acquisition of the extremely low magnificationimage is ended (STEP 1609).

Since the frame-integrated image of the region 1 (1701) is now acquired,the information processing unit 117 moves the stage to the next region 2(1702) via the stage control unit 118 (STEP 1608).

Thereafter, STEP 1605 to STEP 1608 are repeated until theframe-integrated image of region 16 (1703) is acquired. For example, asillustrated in FIG. 26, the image processing unit 113 acquiresframe-integrated images along the order of dotted arrows. After theframe-integrated image of the entire region is acquired, the informationprocessing unit 117 transfers image data of the entire region to theinformation transmission apparatus 121.

Next, the operation flow of FIG. 28 will be described together with theoperation of the screen of FIG. 27. The screen 1801 includes an imagedisplay window 1802, an extremely low magnification image settingportion 1803, a division number setting portion 1804, an integrationmode setting portion 1805, and an image acquisition execution button1807.

When the observation region for which an extremely low magnificationimage is intended to be determined is determined, the user sets the sizeand coordinates of the extremely low magnification image in theextremely low magnification image setting portion 1803 (STEP 1901).Next, the user sets the division number of the image in the divisionnumber setting portion 1804. In the present example, the division numberis set to 16 (STEP 1902). The user may set the size of the divided imagein the division number setting portion 1804. In this case, the regionwhich is set in the extremely low magnification image setting portion1803 is divided by the designated image size.

Next, a scanning method of the divided image is set. In general, as amethod of integrating images, there are a method of integrating incontinuous time in pixel units and a method of integrating in units offrames. In this example, since frame integration becomes a target, acase of setting the frame integration number is described. The userselects the frame integration mode in the integration mode settingportion 1805, and sets the integration number in the integration numbersetting portion 1806 (STEP 1903). Accordingly, the same integrationnumber is set for all the divided regions. The number of scanning linesand the size of the horizontal pixel when acquiring a divided image arethe same as those described in PTL 6. The information processing unit117 automatically calculates the number of scanning lines and thehorizontal pixel size based on information of the division numbersetting portion 1804.

When various setting described above is completed, the user clicks theimage acquisition execution button 1807 to execute acquisition of theextremely low magnification image (STEP 1904). When the frame-integratedimages of all the divided regions are acquired by the flow described inFIG. 25, the information processing unit 117 transfers theseframe-integrated images to the display device of the informationtransmission apparatus 121. The extremely low magnification image isdisplayed on the image display window 1802 (STEP 1905). As illustratedin FIG. 27, in the image display window 1802, the frame-integratedimages of all the divided regions are displayed in a form joinedtogether.

Next, the user confirms the extremely low magnification image of theimage display window 1802 (STEP 1906). Here, in a case where theobtained extremely low magnification image is an image having imagequality expected by the user, acquisition of the low magnification imageis ended (STEP 1907). On the other hand, in a case where the acquiredextremely low magnification image is not an image having image qualityexpected by the user, the integration number needs to be set again toacquire the frame-integrated image of the region which becomes a target.In FIG. 27, an image having image quality that is not expected by theuser is acquired in a divided region 1808, and an image having an imagequality expected by the user is acquired in another divided region 1809.As such, when an image that is not expected by the user is included inthe extremely low magnification image, the integration number needs tobe set again to acquire the frame-integrated image of the region whichbecomes the target. That is, the user needs to repeat STEP 1903 to STEP1906 until an extremely low magnification image to be expected isobtained.

In this example, the same integration number is uniformly set for allthe divided regions, but a method of setting the integration number foreach region is also conceivable. However, as described above, the frameintegration number to be set is greatly influenced by the compositionelements and structures of the sample, and observation conditions(accelerating voltage, irradiation yield, degree of vacuum, WD, and thelike). For that reason, it is difficult to ascertain the optimumintegration number considering the structure of the sample andobservation condition in advance when the frame-integrated image isacquired. Accordingly, conventionally, cases where the operations ofSTEP 1903 to STEP 1906 are repeated to obtain the optimum integrationnumber to acquire the frame-integrated image often occur.

As a result, conventionally, there were the following problems.

(a) It takes time and effort to perform repetitive image acquisition.

(b) Since image acquisition is repeatedly performed, the imageacquisition time increases.

(c) The electron beam irradiation time for the sample is increased(electron beam irradiation amount increases) by the b. There is a highpossibility of causing secondary problems such as an increase in theamount of electron beams with which the sample is to be irradiated,causing sample destruction, causing occurrence of contamination, andcharging the sample. In particular, as the number of divided regions Mincreases, the above problem increases by M times.

In the following, embodiments for solving the above problem will bedescribed. An example of the charged particle beam apparatusconfiguration according to the present embodiment is the same as that inFIG. 6 and thus, description thereof is omitted. Frame integrationprocessing here is the same as that described with reference to FIGS. 7and 8.

In the following description, a scanning electron microscope, which isan example of a charged particle beam apparatus, will be described as anexample, but is not limited thereto. The present invention can also beapplied to other charged particle beam devices such as an ion beamdevice for combining secondary signals such as images to form a combinedsignal.

Means for realizing an image processing part in the following embodimentmay be subjected to function realization by software or by hardware. Inthe following example, function realization by hardware will bedescribed.

Each of the plurality of divided regions in the sample 507 is irradiatedwith the electron beam 503 in the electron beam optical system and theimage processing unit 513 outputs the integrated image obtained by thenormalization integration computation with respect to each of theplurality of divided regions. The image processing unit 513 updates theintegrated image on the display unit of the information transmissionapparatus 521 according to the number of times of execution ofintegration processing (normalization integration computation) for eachof the plurality of divided regions. The image processing unit 513determines the end of integration processing according to image qualityof the integrated image for each of the plurality of divided regions.

In detail, the image processing unit 513 repeatedly executes thenormalization integration computation until the evaluation condition foreach of the plurality of divided regions is satisfied. That is, after animage having image quality expected by the user is obtained for onedivided region, it moves to the next divided region. Since the imageevaluation is performed in each of the plurality of divided regions andthe end of the normalization integration computation is determined,there is a case where the number of times of execution (that is, theintegration number of integrated images) of the normalizationintegration computation is different among the plurality of dividedregions.

FIG. 29 illustrates the processing flow for creating an extremely lowmagnification image according to the present embodiment, and FIG. 30illustrates the outline of scanning for creating the extremely lowmagnification image. FIG. 31 illustrates a GUI when the extremely lowmagnification image is acquired and FIG. 32 illustrates an operationflow when an extremely low magnification image is obtained.

A screen 2201 is displayed on the display device of the informationtransmission apparatus 521. The user decides the observation region forwhich the frame-integrated image is intended to be acquired, performsvarious setting, and then executes low magnification image acquisition(STEP 2001). When an execution instruction is received, the informationprocessing unit 517 moves the sample stage (stage) 508 to the initialcoordinates via the stage control unit 518 based on coordinate data seton the screen 2201 (STEP 2002).

Next, the information processing unit 517 sets the number of scanninglines in the deflection control unit 519 (STEP 2003). Next, theinformation processing unit 517 sets the recording range of the framememory 514 (STEP 2004). The information processing unit 517 sets therecording start point of the frame memory 514 in the regioncorresponding to the stage position described above (STEP 2005).

Next, the image processing unit 513 executes the frame normalizationintegration computation (FIGS. 7 and 8) described in the firstembodiment, and stores the frame-integrated image in the frame memory514 (STEP 2006). FIG. 30 illustrates an example in which the sample isdivided into a plurality of regions. In this example, the sample isdivided into 16 regions. The image acquisition target region at thistime is region 1 (2101). The image processing unit 513 executes theframe normalization integration computation (FIGS. 7 and 8) described inthe first embodiment for the region 1 (2101).

When the frame-integrated image acquisition is completed, theinformation processing unit 517 confirms whether the stage position isthe final region 16 (2103) or not (STEP 2007). In a case where it is thefinal region 16 (2103), acquisition of the extremely low magnificationimage is ended (STEP 2009).

Since the frame-integrated image of the region 1 (2101) is now acquired,the information processing unit 517 moves the stage to the next region 2(2102) via the stage control unit 118 (STEP 2008).

Thereafter, STEP 2005 to STEP 2008 are repeated until theframe-integrated image of region 16 (2103) is acquired. For example, asillustrated in FIG. 30, the image processing unit 513 acquiresframe-integrated images along the order of dotted arrows. In thisexample, after the frame-integrated image of the entire region isacquired, the information processing unit 517 transfers image data ofthe entire region to the information transmission apparatus 521. Asanother example, the information processing unit 517 may transfer theframe-integrated image to the information transmission apparatus 521every time the frame normalization integration computation is completed.As another example, the information processing unit 517 may transfer theframe-integrated image to the information transmission apparatus 521when the frame normalization integration computation is completed in onedivided region (at the time when the image having image quality expectedby the user is obtained).

Next, the operation flow of FIG. 32 will be described together with theoperation of the screen of FIG. 31. The screen 2201 includes an imagedisplay window 2202, an extremely low magnification image settingportion 2203, a division number setting portion 2204, an integrationmode setting portion 2205, an image acquisition execution button 2207,and an evaluation method setting button 2208.

When the observation region for which an extremely low magnificationimage is intended to be determined is determined, the user sets the sizeand coordinates of the extremely low magnification image in theextremely low magnification image setting portion 2203 (STEP 2301).Next, the user sets the division number of the image in the divisionnumber setting portion 2204. In the present example, the division numberis set to 16 (STEP 2302). The user may set the size of the divided imagein the division number setting portion 2204. In this case, the regionwhich is set in the extremely low magnification image setting portion2203 is divided by the designated image size.

Next, a scanning method of the divided image is set. In general, as amethod of integrating images, there are a method of integrating incontinuous time in pixel units and a method of integrating in units offrames. In this example, since frame integration becomes a target, acase of setting the frame integration number is described. The userselects the frame integration mode and sets the integration number inthe integration number in the integration mode setting portion 2205(STEP 2303). The number of scanning lines and the size of the horizontalpixel when acquiring a divided image are the same as those described inPTL 6. The information processing unit 517 automatically calculates thenumber of scanning lines and the horizontal pixel size based oninformation of the division number setting portion 2204.

In the integration mode setting portion 2205, it is possible to selecteither the automatic mode or the integration number designation mode.The automatic mode is a mode for performing automatic evaluation by theimage evaluation unit 522. The user sets an image evaluation method in acase of selecting the automatic mode. The user clicks the evaluationmethod setting button 2208. The window displayed when the evaluationmethod setting button 2208 is clicked is the evaluation method settingwindow 1001 illustrated in FIG. 13. The method of selecting theevaluation method is the same as that of the first example, and thusdescription thereof will be omitted.

The integration number designation mode is a mode in which a frameintegration number is designated in advance. In the case of theintegration number designation mode, the user inputs the integrationnumber to the integration number setting portion 2206. In this case,integration processing may be executed up to the set integration number,and the integrated image may be evaluated by the user himself/herself.As another example, at the time when integration processing is executedframe by frame and an integrated image displayed in the image displaywindow 2202 becomes image quality expected by the user, a function ofstopping integration processing by the user's input and moving to thenext divided region may be provided.

When various setting described above is completed, the user clicks theimage acquisition execution button 2207 to execute acquisition of anextremely low magnification image (STEP 2304). When the frame-integratedimages of all the divided regions are acquired by the flow described inFIG. 29, the information processing unit 517 transfers theseframe-integrated images to the display device of the informationtransmission apparatus 521. In the image display window 2202, theextremely low magnification image is displayed (STEP 2305). Asillustrated in FIG. 31, in the image display window 2202,frame-integrated images of all the divided regions are displayed in aform of being joined together. Here, the frame-integrated image of eachdivided region is evaluated by the selected evaluation method and isintegrated until the evaluation reference value is satisfied.Accordingly, in all the divided regions of the image display window2202, images having image quality expected by the user are acquired. Bythe operation described above, acquisition of the extremely lowmagnification image is ended (STEP 2306).

On the screen 2201, the number of times of executions (that is, theintegration number) of frame normalization integration computation ofeach divided region, the evaluation value of each divided region, andthe like may be displayed. The user can confirm the difference in thenumber of times of execution of the normalization integrationcomputation among the plurality of divided regions, the difference inthe evaluation value among the plurality of divided regions, and thelike.

In the conventional extremely low magnification image acquisition, in acase where the displayed extremely low magnification image is confirmedand an image which does not have image quality expected by the user isincluded, it is necessary to set the integration number again andrepeatedly acquire the repeated integrated image. In contrast, in thepresent embodiment, similarly as in the first embodiment, it is possibleto acquire an extremely low magnification image having image qualityexpected by the user by one image acquisition operation.

As illustrated in the operation flow illustrated in FIG. 32, the usercan acquire the extremely low magnification image only by the operationof “image acquisition execution” without being never conscious of thesetting of the integration number. With this, it is possible to greatlyimprove time and effort for acquiring the extremely low magnificationimage. The time spent on image acquisition can also be greatly reduced.

The present embodiment has the following effects.

(a) In contrast to the conventional plural image acquisition operations,in the present embodiment, a frame-integrated image is obtained by oneimage acquisition operation.

(b) In the present embodiment, it is possible to perform the integrationscan with the minimum required number of integration by one imageacquisition operation.

(c) By both effects described above, it is possible to reduce theirradiation time of the electron beam with which the sample isirradiated as much as possible.

(d) By suppressing the amount of electron beam with which the sample isirradiated to be minimized, it is possible to obtain secondary effectsthat suppresses sample destruction, contamination generation, generationof luminance value saturation and drift due to the influence of chargingto be minimized.

In a case where it is applied to the extremely low magnification imageacquisition function, the effects described above increases by M timesaccording to the number M of division regions.

In the automatic mode, in order to avoid that the evaluation value doesnot reach the evaluation reference value even if integration processingis repeated and the frame-integrated image cannot be acquired forever,an upper limit value of the integration number may be set in theinformation processing unit 517. In a case where the upper limit valueof the integration number reaches the upper limit value (in a case wherea count value of the integration counter 601 reaches the upper limitvalue), the information processing unit 517 may forcibly end acquisitionof the integrated image. For ease of use, it is also possible toconsider a case the user may want to acquire an integrated image with aslittle noise as possible by setting the integration number to large. Inthis case, the upper limit of the number of integration may be set tolarge.

In the present embodiment, when the frame-integrated images of all thedivided regions are acquired, the information processing unit 517transfers image data of all the divided regions to the informationtransmission apparatus 521. The transferred image data is displayed onthe image display window 2202. As another example, the informationprocessing unit 517 may transfer image data to the informationtransmission apparatus 521 at the time when acquisition of theframe-integrated image of each division region is completed. Thetransferred image data of each divided region may be sequentiallydisplayed in the image display window 2202. By adopting this displaysystem, the user can know the acquisition situation of extremely lowmagnification image acquisition and the difference in frame integrationnumber for each division region, thereby improving usability for a user.

Third Embodiment

In the second embodiment, the extremely low magnification image creationfunction which sequentially completes the frame normalizationintegration computation for each divided region (that is, a method ofcompleting the frame normalization integration computation for eachregion from region 1 to region 16) is described. In the presentembodiment, an extremely low magnification image creation function thatprocesses all the divided regions in parallel by sequentially processingthe frame normalization integration computation in each divided regionintegration computation by integration computation will be described.

As described above, the frame integration number to be set is greatlyinfluenced by composition elements and structures of the sample andobservation conditions (accelerating voltage, irradiation yield, degreeof vacuum, working distance (WD), and the like). Here, it is generallyknown that these observation conditions are influenced by disturbance ina peripheral environment of apparatus such as temperature, vibration,electric field, and magnetic field and a slight change occurs in theoptical characteristics. That is, there is concern that the frameintegration number may also be influenced by the disturbance of theperipheral environment of apparatus.

That is, in the extremely low magnification image creation functiondescribed in the second embodiment, in a short period of time within aperiod of time from the start of the integrated image acquisition of theregion 1 to the completion of the integrated image acquisition of thefinal region 16, in a case where “vibration”, for example, greatlyfluctuates in the peripheral environment of apparatus, in the method ofthe second embodiment, the region just under the integration computationat the time of the fluctuation is greatly influenced by the “vibration”.As a result, there is concern that only in that region, image quality isbad, noise is added, and the integration number is extremely increased.Accordingly, as a method to smooth this influence as much as possible,an example of an extremely low magnification image creation function ofthe present embodiment is proposed.

Also, attention is paid to charge of the sample. In the frame-integratedimage acquisition of the second embodiment, a plurality of frame imagesare acquired in each divided region in order to acquire aframe-integrated image in each divided region. Here, in order to acquirethe first frame image, a frame scan is performed to acquire a frameimage. Thereafter, in order to acquire the second frame image, secondframe scan is performed to acquire a second frame-integrated image. Assuch, the process described above is repeated until an image index(evaluation reference value) defined by the user is satisfied. Thismeans that the frame scan is continuously executed on the same sampleregion until a frame-integrated image satisfying the image index can beconstructed. Here, in the case of a sample that is easy to charge, thereis concern that the sample will be charged by continuous beamirradiation and luminance value saturation and drift due to the changewill occur. The extremely low magnification image creation function ofthe third embodiment also exhibits an effective effect against thisproblem.

FIG. 33 illustrates a processing flow of creation of an extremely lowmagnification image according to the present embodiment, and FIGS. 34 to39 illustrate an outline of scanning for creating an extremely lowmagnification image. FIG. 40 illustrates a GUI for acquiring anextremely low magnification image.

The image processing unit 513 updates the integrated image on thedisplay unit of the information transmission apparatus 521 according tothe number of times of execution of integration processing(normalization integration computation) for each of the plurality ofdivided regions. The image processing unit 513 determines the end ofintegration processing according to the image quality of the integratedimage for each of the plurality of divided regions.

More specifically, the image processing unit 513 executes thenormalization integration computation once for each of the plurality ofdivided regions. The image processing unit 513 executes thenormalization integration computation only for the divided regions thatdo not satisfy the evaluation condition on the next time and thereafter.In the following, the first, second, (M−1)-th, and M-th normalizationintegration computation the will be described.

A screen 2601 is displayed on the display device of the informationtransmission apparatus 521. The user decides the observation region forwhich the frame-integrated image is intended to be acquired, performsvarious settings, and then executes the low magnification imageacquisition (STEP 2401). When the execution instruction is received, theinformation processing unit 517 moves the sample stage (stage) 508 tothe initial coordinates via the stage control unit 518 based oncoordinate data which is set on the screen 2601 (STEP 2402).

Next, the information processing unit 517 sets the number of scanninglines in the deflection control unit 519 (STEP 2403). Next, theinformation processing unit 517 sets the recording range of the framememory 514 (STEP 2404).

<Acquisition of First Integrated Image>

A case of acquiring the first integrated image will be described withreference to FIGS. 34 and 35. The information processing unit 517determines whether acquisition of the frame-integrated image iscompleted in a target divided region (STEP 2405). Since it is nowimmediately after the start of extremely low magnification imageacquisition and the image of the first frame of region 1 (2501) is notacquired, the information processing unit 517 sets a recording startpoint of the frame memory 514 in a region corresponding to the region 1(2501) coordinates (STEP 2406).

Next, the frame scan is executed once and the image processing unit 513acquires image data. The image processing unit 513 executes the framenormalization integration computation (FIGS. 7 and 8) described in thefirst embodiment. Here, because it is the image of the first frame, theimage processing unit 513 outputs the acquired image as it is to theframe memory 514, the information processing unit 517, and the imageevaluation unit 522. Image data 2511 is stored in the frame memory 514as integrated image data of the first frame (integrated image data towhich integration is applied once). The image evaluation unit 522evaluates the input image data 2511 (STEP 2409). Here, it is assumedthat the image data 2511 of the region 1 (2501) is an image that doesnot having image quality expected by the user. The informationprocessing unit 517 determines that acquisition of the frame-integratedimage of the region 1 (2501) is incomplete.

The image data 2511 output to the information processing unit 517 istransferred to the information transmission apparatus 521. In an imagedisplay window 2602, the image data 2511 is displayed as an integratedimage being integrated. Next, the information processing unit 517determines whether the stage position is the final position, that is,the region 16 (2503) or not (STEP 2411). Since the image of the region 1(2501) is now acquired, the information processing unit 517 moves thestage to the next region 2 (2502) via the stage control unit 518 (STEP2412). Thereafter, STEP 2405 to STEP 2412 described above are repeatedto acquire image data 2512 of the region 2 (2502) to image data 2513 ofthe region 16 (2503).

Here, as illustrated in FIG. 35, it is assumed that integrated imagedata acquired in the first the frame scan is not the image having imagequality expected by the user in any region of 16 regions of an extremelylow magnification image 2510. After image data 2513 of the region 16(2503) is acquired, the information processing unit 517 determineswhether acquisition of the integrated image is completed in all regions(STEP 2413). In this case, since an image that does not having imagequality expected by the user is obtained in any region, the informationprocessing unit 517 moves the stage to the initial position 2501 via thestage control unit 518 (STEP 2414).

<Acquisition of Second Integrated Image>

Next, a case of acquiring a second integrated image will be describedwith reference to FIG. 36. STEP 2405 to STEP 2412 described above arerepeated. The information processing unit 517 determines whetheracquisition of the frame-integrated image is completed in a dividedregion which becomes a target (STEP 2405). Here, since the acquisitionof the frame-integrated image of the region 1 (2501) is not completed,the information processing unit 517 sets the recording start point ofthe frame memory 514 in the region corresponding to the region 1 (2501)coordinates (STEP 2406).

Next, the frame scan is executed once and the image processing unit 513acquires image data. The image processing unit 513 executes the framenormalization integration computation (FIGS. 7 and 8) described in thefirst embodiment. The image processing unit 513 executes the framenormalization integration computation of image data detected by thecurrent the frame scan and image data which is stored in the framememory 514 and corresponds to the region 1 (2501).

The image processing unit 513 outputs image data (frame-integratedimage) 2521 to the frame memory 514, the information processing unit517, and the image evaluation unit 522. The image data 2521 is stored inthe frame memory 514 as integrated image data of the second frame(integrated image data to which integration is applied twice). The imageevaluation unit 522 evaluates the input image data 2521 (STEP 2409).Here, it is assumed that the image data 2521 of the region 1 (2501) isan image that does not have image quality expected by the user. Theinformation processing unit 517 determines that acquisition of theframe-integrated image of the region 1 (2501) is incomplete.

The image data 2521 output to the information processing unit 517 istransferred to the information transmission apparatus 521. In the imagedisplay window 2602, the image data 2521 is displayed as an integratedimage being integrated. Next, the information processing unit 517determines whether the stage position is the final position, that is,the region 16 or not (2503) (STEP 2411). Since the image of the region 1(2501) is now acquired, the information processing unit 517 moves to thenext region 2 (2502) via the stage control unit 518 (STEP 2412).Thereafter, STEP 2405 to STEP 2412 described above are repeated toacquire image data 2522 of the region 2 (2502) to image data 2523 ofregion 16 (2503).

Here, as illustrated in FIG. 36, it is assumed that the secondframe-integrated image data is an image that does not have image qualityexpected by the user in any region of 16 regions of an extremely lowmagnification image 2520. After image data 2523 of the region 16 (2503)is acquired, the information processing unit 517 determines whetheracquisition of the integrated image is completed in all regions (STEP2413). Here, since an image that does not have image quality expected bythe user is obtained in any region, the information processing unit 517moves the stage to the initial position 2501 via the stage control unit518 (STEP 2414).

<Acquisition of (M−1)-th Integrated Image>

Thereafter, a case where STEP 2405 to STEP 2414 are repeated a pluralityof times to acquire an (M−1)-th integrated image will be described withreference to FIG. 37. The information processing unit 517 determineswhether acquisition of the frame-integrated image is completed in thedivided region which becomes a target (STEP 2405). Here, since theacquisition of the frame-integrated image of the region 1 (2501) is notcompleted, the information processing unit 517 sets the recording startpoint of the frame memory 514 in the region corresponding to the region1 (2501) coordinates (STEP 2406).

Next, the frame scan is executed once, and the image processing unit 513acquires image data. The image processing unit 513 executes the framenormalization integration computation (FIGS. 7 and 8) described in thefirst embodiment. The image processing unit 513 executes the framenormalization integration computation of image data detected by thecurrent the frame scan and image data stored in the frame memory 514corresponding to the region 1 (2501).

The image processing unit 513 outputs image data (frame-integratedimage) 2531 to the frame memory 514, the information processing unit517, and the image evaluation unit 522. The image data 2531 is stored inthe frame memory 514 as integrated image data of the (M−1)-th frame(integrated image data to which integration is applied (M−1) times). Theimage evaluation unit 522 evaluates the input image data 2531 (STEP2409). Here, it is assumed that the image data 2531 of the region 1(2501) is an image having image quality expected by the user. Theinformation processing unit 517 determines that acquisition of theintegrated image in the region 1 (2501) is completed. The informationprocessing unit 517 stores in a storing unit of the informationprocessing unit 517 that acquisition of the frame-integrated image ofthe region 1 (2501) is completed (STEP 2410).

The image data 2531 output to the information processing unit 517 istransferred to the information transmission apparatus 521. In the imagedisplay window 2602, the image data 2531 is displayed as an integratedimage being integrated. Next, the information processing unit 517determines whether the stage position is the final position, that is,the region 16 (2503) or not (STEP 2411). Since the image of the region 1(2501) is now acquired, the information processing unit 517 moves thestage to the next region 2 (2502) via the stage control unit 518 (STEP2412). Thereafter, STEP 2405 to STEP 2412 described above are repeatedto acquire image data 2532 of the region 2 (2502) to image data 2533 ofthe region 16 (2503).

Here, as illustrated in FIG. 37, it is assumed that if the image data2531 of the region 1, image data 2534 of the region 7, image data 2535of the region 8, and image data 2536 of the region 9 are images havingimage quality expected by the user. After the image data 2533 of theregion 16 (2503) is acquired, the information processing unit 517determines whether acquisition of the integrated image is completed inall regions of the extremely low magnification image 2530 (STEP 2413).Here, since the image having image quality expected by the user is stillnot obtained in all regions of the extremely low magnification image2530, the information processing unit 517 moves the stage to the initialposition 2501 via the stage control unit 518 (STEP 2414).

<Acquisition of M-th Integrated Image>

Next, a case of acquiring an M-th integrated image will be describedwith reference to FIG. 38. STEP 2405 to STEP 2412 described above arerepeated. The information processing unit 517 determines whetheracquisition of the frame-integrated image is completed in the dividedregion which becomes the target (STEP 2405). Here, since acquisition ofthe frame-integrated image of the region 1 (2501) is completed, theinformation processing unit 517 moves the stage to the next region 2(2502) via the stage control unit 518 (STEP 2407). As described above,the region where acquisition of the frame-integrated image is completedis skipped, and a frame-integrated image is acquired only for the regionfor which acquisition of the frame-integrated image is not completed.

Next, the information processing unit 517 determines whether acquisitionof the frame-integrated image is completed in the region 2 or not (2502)(STEP 2405). Here, since acquisition of the frame-integrated image ofthe region 2 (2502) is not completed, the information processing unit517 sets the recording start point of the frame memory 514 in the regioncorresponding to the region 2 (2502) coordinates (STEP 2406).

Next, the frame scan is executed once, and the image processing unit 513acquires image data. The image processing unit 513 executes the framenormalization integration computation (FIGS. 7 and 8) described in thefirst embodiment. The image processing unit 513 executes the framenormalization integration computation of image data detected by thecurrent frame scan and image data stored in the frame memory 514corresponding to the region 2 (2502).

The image processing unit 513 outputs image data (frame-integratedimage) 2542 to the frame memory 514, the information processing unit517, and the image evaluation unit 522. The image data 2542 is stored inthe frame memory 514 as integrated image data of the M-th frame(integrated image data to which integration is applied M times). Theimage evaluation unit 522 evaluates the input image data 2542 (STEP2409). Here, it is assumed that the image data 2542 of the region 2(2502) is an image that does not have image quality expected by theuser. The information processing unit 517 determines that acquisition ofthe frame-integrated image of the region 2 (2502) is incomplete.

The image data 2542 output to the information processing unit 517 istransferred to the information transmission apparatus 521. On the imagedisplay window 2602, the image data 2542 is displayed as an integratedimage being integrated. Next, the information processing unit 517determines whether the stage position is the final position, that is,the region 16 (2503) or not (STEP 2411). Since the image of the region 2(2502) is now acquired, the information processing unit 517 moves thestage to the next region 3 via the stage control unit 518 (STEP 2412).Thereafter, STEP 2405 to STEP 2412 described above are repeated untilimage data 2543 of the region 16 (2503) is acquired. However, asdescribed above, acquisition of the image data 2534 of the region 7, theimage data 2535 of the region 8, and the image data 2536 of the region 9is been completed. Accordingly, the regions 7, 8 and 9 are skipped, andimage data of the regions 3 to 6 and 10 to 16 which do not satisfy theevaluation condition are acquired (dotted arrow 2548).

FIG. 39 illustrates an extremely low magnification image 2550 for whichacquisition of the frame-integrated image is completed in all thedivided regions. In the present embodiment, it is possible to constructan extremely low magnification image 2550 which becomes to have imagequality expected by the user in all the regions.

In the example described above, the movement between the divided regionsis executed by the stage, but is not limited thereto. An irradiationposition of the electron beam may be moved by the deflection coil 505 aslong as it is within a range changeable by deflection by the deflectioncoil 505. Also, the movement between the divided regions may beperformed using both the stage and the deflector.

The operation flow when acquiring an extremely low magnification imageis the same as that in FIG. 32 and thus, description thereof will beomitted. FIG. 40 illustrates a GUI when acquiring an extremely lowmagnification image. A screen 2601 includes an image display window2602, an extremely low magnification image setting portion 2603, adivision number setting portion 2604, an integration mode settingportion 2605, an image acquisition execution button 2607, and anevaluation method setting button 2608. The constituent elements 2602 to2608 of the screen 2601 are the same as the constituent elements 2202 to2208 of the screen 2201 of FIG. 31 and thus, description thereof will beomitted.

On the screen 2601, the number of times of execution (that is, theintegration number) of the frame normalization integration computationof each divided region, the evaluation value of each divided region, andthe like may be displayed.

As in the operation flow illustrated in FIG. 32, the user can acquire anextremely low magnification image only by operation of “imageacquisition execution” without being never conscious of setting of theintegration number. With this, it is possible to greatly improve timeand effort for acquiring the extremely low magnification image. It ispossible to greatly reduce the time required for image acquisition.

The present embodiment has the following effects.

(a) In contrast to the conventional plural image acquisition operations,in the present embodiment, a frame-integrated image is obtained by oneimage acquisition operation.

(b) In the present embodiment, it is possible to perform the integrationscan with the minimum required number of integration by one imageacquisition operation.

(c) By both effects described above, it is possible to reduce theirradiation time of the electron beam with which the sample isirradiated as much as possible.

(d) By suppressing the amount of electron beam with which the sample isirradiated to be minimized, it is possible to obtain secondary effectsthat suppresses sample destruction, contamination generation, generationof luminance value saturation and drift due to the influence of chargingto be minimized.

In a case of being applied to the extremely low magnification imageacquisition function, the above problem increases by M times accordingto the number M of division regions.

The present embodiment corresponds to the extremely low magnificationimage creation function of sequentially processing integrationcomputations in each divided region one integration computation by oneintegration computation so as to process all regions in parallel. Asdescribed above, the frame integration number is influenced by thedisturbance in the peripheral environment of apparatus. In a shortperiod of time within a period of time from the start of the integratedimage acquisition to the completion of the integrated image acquisition,in a case where “vibration”, for example, greatly fluctuates in theperipheral environment of apparatus, the region just under theintegration computation at the time of the fluctuation is greatlyinfluenced by the “vibration”, in the method of the second embodiment.As a result, there is concern that only in that region, image quality isbad, noise is added, and the integration number is extremely increased.

In the acquisition method of the present embodiment, a possibility thatthe influence can be dispersed as much as possible to a plurality ofregions can be expected, and as a result, it is possible to smoothfluctuation of disturbance in the plurality of regions. Not onlyfluctuations in a short period of time but also, for example, even whenthe surrounding “temperature” of the apparatus fluctuates slowly over along period of time, the influence of fluctuation can be smoothed in theplurality of regions by the same mechanism as described above.

As described above, the present embodiment has an advantage that it ispossible to acquire a stable integrated image with little difference inthe influence of fluctuation between the regions by smoothing theinfluence of fluctuation of the disturbance around the apparatus incomparison with the second embodiment. When attention is paid to chargeof the sample, in the frame-integrated image acquisition of the secondembodiment, the frame scan is continuously executed for the same regionuntil the frame integration image satisfying the image index can beconstructed in each of the divided regions. In the case of a samplewhich is easy to charge, there is a possibility of charging due to thiscontinuous beam irradiation and generating saturation of luminance valueand drift due to charging. In the present embodiment, since integrationcomputation is performed one integration computation by one integrationcomputation for each of the divided regions, it is intermittent beamirradiation from the viewpoint of each region. That is, chargegeneration can be suppressed, and an effect of charge reduction can alsobe obtained.

In the automatic mode, in order to avoid that the evaluation value doesnot reach the evaluation reference value even if integration processingis repeated and the frame-integrated image cannot be acquired forever,an upper limit value of the integration number may be set in theinformation processing unit 517. In a case where the upper limit valueof the integration number reaches the upper limit value (in a case wherea count value of the integration counter 601 reaches the upper limitvalue), the information processing unit 517 may forcibly end acquisitionof the integrated image. For ease of use, it is also possible toconsider a case the user may want to acquire an integrated image with aslittle noise as possible by setting the integration number to large. Inthis case, the upper limit of the number of integration may be set tolarge.

In the present embodiment, an example in which each divided region isscanned by moving a scan table is described, but is not limited to thisexample, and coordinate control of the region may be performed byanother method, for example, using a coil or a lens.

In the present embodiment, an example in which the integrated image isdisplayed on the image display window 2602 at any time during theintegration is described. By displaying the integrated image beingintegrated at any time in the image display window, the user can confirmthe process in which an image of the entire region is graduallyconstructed (process of being integrated) in real time. There is anadvantage that it is possible to visually ascertain the process of theintegration situation and the degree of integration. In the presentembodiment, an example in which the integrated image is displayed on theimage display window 2602 at any time during the integration isdescribed, but is not limited thereto. The integrated images of all theregions may be displayed in the image display window 2602 all togetherafter completion of construction.

The present invention is not limited to the embodiments described above,but includes various modification examples. The embodiments describedabove have been described in detail in order to explain the presentinvention in an easy-to-understand manner, and are not necessarilylimited to those having all the configurations described. A portion ofthe configuration of a certain example can be replaced by theconfiguration of another example. The configuration of another examplecan be added to the configuration of a certain example. It is possibleto add, delete, and replace other configurations for a portion of theconfiguration of each example.

Each of the configurations, functions, processing units, processingmeans, and the like described above may be realized in hardware bydesigning a portion or all of them with, for example, an integratedcircuit. Each of configurations, functions, and the like described abovemay be realized by software by allowing a processor to interpret andexecute a program which realizes each function. Information such asprograms, tables, files, and the like that realize each function can bestored in various types of non-transitory computer readable medium. Asthe non-transitory computer readable medium, for example, a flexibledisk, a CD-ROM, a DVD-ROM, a hard disk, an optical disk, amagneto-optical disk, a CD-R, a magnetic tape, a nonvolatile memorycard, a ROM, and the like are used.

In the embodiments described above control lines and information linesindicate what is considered to be necessary for explanation, and do notnecessarily indicate all control lines and information lines forproducts. All the configurations may be connected to each other.

REFERENCE SIGNS LIST

-   -   501: vacuum column    -   502: electron gun (charged particle beam source)    -   503: electron beam (charged particle beam)    -   504: focusing lens    -   505: deflection coil    -   506: objective lens    -   507: sample    -   508: sample stage    -   510: detector    -   511: amplifier    -   512: ADC    -   513: image processing unit    -   514: frame memory    -   515: multiplier    -   516: adder    -   517: information processing unit    -   518: stage control unit    -   519: deflection control unit    -   520: information input device    -   521: information transmission apparatus    -   522: image evaluation unit    -   523: multiplier    -   524: deflection signal    -   525: control signal    -   526: image evaluation result    -   527: image data

The invention claimed is:
 1. A charged particle beam device comprising:a charged particle beam source; a charged particle beam optical systemthat irradiates a sample with a charged particle beam from the chargedparticle beam source; a detector that outputs a signal caused byirradiation with the charged particle beam; an image processing unitthat executes integration processing of image data obtained from thesignal and outputting an integration image; and a display unit thatdisplays the integrated image output during integration, wherein theimage processing unit executes integration computation of a luminancevalue and changes a coefficient of the integration based on a framecount value of the integration.
 2. The charged particle beam deviceaccording to claim 1, wherein the image processing unit includes astoring unit that stores the integrated image, a first multiplier thatoutputs first image data obtained by multiplying the image data obtainedfrom the signal by a first coefficient, a second multiplier that outputssecond image data obtained by multiplying one previous integrated imageby a second coefficient, and an adder that adds the first image data andthe second image data and outputs the integrated image, wherein thefirst coefficient and the second coefficient vary according to thenumber of times of execution of the integration computation and a sum ofthe first coefficient and the second coefficient is “1”.
 3. The chargedparticle beam device according to claim 1, further comprising: an imageevaluation unit that determines whether the integrated image obtained bythe integration computation satisfies a certain evaluation condition,wherein the image processing unit repeatedly executes the integrationcomputation until the evaluation condition is satisfied.
 4. The chargedparticle beam device according to claim 3, wherein the evaluationcondition includes at least one of a condition with an SN ratio as anevaluation index, a condition with a degree of SN improvement as anevaluation index, a condition with a CNR as an evaluation index, and acondition with a luminance value histogram as an evaluation index. 5.The charged particle beam device according to claim 3, furthercomprising: a display unit that displays the integrated image after theintegration computation and a setting unit for setting the evaluationcondition.
 6. The charged particle beam device according to claim 1,wherein the charged particle beam optical system irradiates each of aplurality of divided regions in the sample with the charged particlebeam, and the image processing unit outputs the integrated imageobtained by the integration computation to each of the plurality ofdivided regions.
 7. The charged particle beam device according to claim6, wherein the number of times of execution of the integrationcomputation is different between the plurality of divided regions. 8.The charged particle beam device according to claim 6, furthercomprising: a display unit that displays the integrated images of allthe divided regions in a joined form.
 9. The charged particle beamdevice according to claim 6, further comprising: an image evaluationunit that determines whether the integrated image obtained by theintegration computation satisfies a certain evaluation condition,wherein the image processing unit repeatedly executes the integrationcomputation until the evaluation condition is satisfied for each of theplurality of divided regions.
 10. The charged particle beam deviceaccording to claim 9, wherein the image processing unit executes theintegration computation once for each of the plurality of dividedregions, and executes the integration computation, on the next time andthereafter, only on the divided region that does not satisfy theevaluation condition.
 11. A charged particle beam device comprising: acharged particle beam source; a charged particle beam optical systemthat irradiates each of a plurality of divided regions in an area to beobserved with a charged particle beam from the charged particle beamsource; a detector that outputs a signal caused by irradiation with thecharged particle beam; an image processing unit that executesintegration processing of image data obtained from the signal andoutputting an integration image; and a display unit that displays theintegrated image output during integration for each of the plurality ofdivided regions, wherein the image processing unit determines end of theintegration processing according to image quality of the integratedimage for each of the plurality of divided regions, and wherein theimage processing unit changes a coefficient of the integration based ona frame count value of the integration.
 12. The charged particle beamdevice according to claim 11, wherein the image processing unit updatesthe integrated image on the display unit for each of the plurality ofdivided regions and ends the integration processing at the time when theintegrated image reaches expected image quality.
 13. The chargedparticle beam device according to claim 11, wherein the number of timesof execution of the integration processing is different between theplurality of divided regions.
 14. The charged particle beam deviceaccording to claim 11, further comprising: an image evaluation unit thatdetermines whether the integrated image of each of the plurality ofdivided regions satisfies a certain evaluation condition, wherein theimage processing unit repeatedly executes the integration processinguntil the evaluation condition is satisfied for each of the plurality ofdivided regions.
 15. The charged particle beam device according to claim14, wherein the image processing unit executes the integrationprocessing once for each of the plurality of divided regions, andexecutes the integration processing, on the next time and thereafter,only on the divided region that does not satisfy the evaluationcondition.
 16. The charged particle beam device according to claim 11,wherein the integration processing is integration computation of aluminance value of the integrated image in an integration process. 17.An image processing method in a charged particle beam device, the imageprocessing method comprising: a step of irradiating a sample with acharged particle beam from a charged particle beam source, by a chargedparticle beam optical system; a step of obtaining a signal caused byirradiation with the charged particle beam from detector; a step ofexecuting integration processing of image data obtained from the signaland outputting an integrated image, by an image processing unit; and astep of displaying the integrated image output during integration,wherein the executing step includes executing integration computation ofa luminance value and changing a coefficient of the integration based ona frame count value of the integration.